[dpdk-dev] [PATCH v7 11/21] eal/soc: implement probing of drivers

[Jianbo Liu]

On 10 November 2016 at 17:26, Thomas Monjalon <thomas.monjalon at 6wind.com> wrote:
> 2016-11-10 14:40, Shreyansh Jain:
>> On Thursday 10 November 2016 01:11 PM, Jianbo Liu wrote:
>> > On 10 November 2016 at 14:10, Shreyansh Jain <shreyansh.jain at nxp.com> wrote:
>> >> On Thursday 10 November 2016 09:00 AM, Jianbo Liu wrote:
>> >>> I'm still not sure about the purpose of soc_scan, and how to use it.
>> >>
>> >>
>> >> For each device to be used by DPDK, which cannot be scanned/identified using
>> >> the existing PCI/VDEV methods (sysfs/bus/pci), 'soc_scan_t' provides a way
>> >> for driver to make those devices part of device lists.
>> >>
>> >> Ideally, 'scan' is not a function of a driver. It is a bus function - which
>> >> is missing in this case.
>> >>
>> >>> If it's for each driver, it should at least struct rte_soc_driver * as
>> >>> its parameter.
>> >>
>> >>
>> >> Its for each driver - assuming that each non-PCI driver which implements it
>> >> knows how to find devices which it can control (for example, special area in
>> >> sysfs, or even platform bus).
>> >>
>> >
>> > Considering there are several drivers in a platform bus, each driver
>> > call the scan function, like the rte_eal_soc_scan_platform_bus() you
>> > implemented.
>> > The first will add soc devices to the list, but the remaining calls
>> > are redundant.
>>
>> Indeed. This is exactly the issue we will face if we try and move this
>> scan/match logic to PCI - all devices are identified in one step.
>>
>> There is a difference in principle here:
>> A SoC device/driver combination is essentially focused towards a single
>> type of bus<->devices. For example, a NXP PMD would implement a scan
>> function which would scan for all devices on NXP's bus. This would not
>> conflict with another XYZ SoC PMD which scans its specific bus.
>>
>> There is caveat to this - the platform bus. There can be multiple
>> drivers which can serve platform bus compliant devices. First
>> PMD->scan() initiated for such a bus/device would leave all other scans
>> redundant.
>>
>> More similar caveats will come if we consider somewhat generic buses. At
>> least I couldn't find any interest for such devices in the ML when I
>> picked this series (from where Jan left it).
>>
>> Probably when more common type of PMDs come in, some default scan
>> implementation can check for skipping those devices which are already
>> added. It would be redundant but harmless.
>
> If several drivers use the same bus, it means the bus is standard enough
> to be implemented in EAL. So the scan function of this bus should be
> called only once when calling the generic EAL scan function.

Agree. rte_eal_soc_scan_platform_bus can be the scanning func for platform bus.